6 Answers
6

This seems to be one of those plural issues where a different plural is used when referring to the large uncountable group. "I found 3 gray hairs this morning" is proper but so is "I washed my hair this morning".

In the second case, your entire head covered with individuals hairs is treated as a single object or group which is why it is referred to in a singular form.

Some of these sound odd. "I just pull out one of your white hair" -> "I just pulled out one of your white hairs". "There are dog hairs on the sofa" -> "There is dog hair on the sofa". "I drop a lot of hairs after operation" -> "I lost a lot of hair after the operation".
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Tester101Jan 25 '11 at 17:57

"I just pull out one of your white hair" still needs to be changed.
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amcnabbMar 22 '12 at 21:49

The the word "hair" in the sentence "I just pulled out one of your white hair" needs to be plural, because the phrase "one of" implies that its object is a collection of a discrete things. If you want to use singular "hair", the sentence should be changed to either "I pulled out a strand of your white hair" or "I pulled out some strands of your white hair".
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supercatOct 10 '14 at 16:50

I think 'Hair' is Material noun. Brick, wood, skin, muscle, oil, glass, paper, paint, gold etc. are all Material Nouns. So, if wish to refer to a particular number of Hair, we should say 3 or 4 strands of hair.

Consider the sentences :

"The other was Della's hair". (not 'hairs')

My hair is turning grey. (not 'hairs are')

My hair is black and his hair is brown. (not 'hairs are')

He caught my wisp or lock of hair. (not 'hairs')

He plucked 10 strands of grey hair from my head. ('10 strands', but not 'hairs')

I think both hair and hairs are right because the sentence "I pulled out some hairs" would be right and "She has a head full of hair" works too, so I think both hair and hairs work that it just depends on the context clues of the sentence.

You are right, but this answer doesn't add anything to what is already here.
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Matt E. Эллен♦Mar 23 '12 at 9:58

I think it is worth noting that the sentence "washing my hairs" could be correct, but would imply that each hair was being washed individually. Such level of detail would be unusual, but in cases where someone's hairs were being washed individually (perhaps the person was nearly bald, and thus only had a few dozen hairs scattered about the head), the plural form of "hairs" would be appropriate.
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supercatOct 10 '14 at 16:55